Method of press molding lens material

Abstract

A lens molding method where a lens material is set between an upper mold and a lower mold, and the molding pressure is reduced or made zero at least once during a heating & pressing step without the mold surfaces breaking contact with the lens materials, and during a cooling & pressing step.

What is claimed is: 
     
       1. A lens molding method for press-molding a body of lens material placed in a space between mold surfaces of a pair of upper and lower molds by applying a molding pressure to the pair of molds to produce a lens, comprising: placing said body of lens material in a space between said mold surfaces;   carrying out a preheating step for heating the body of lens material placed in the space between said mold surfaces of said pair of molds until the temperature of said body rises to a first predetermined temperature;   carrying out a heating and pressing step to apply said molding pressure to said pair of molds having the body of lens material placed therebetween while keeping the temperature of said body at the first predetermined temperature thereby to mold said body into a lens-form body;   carrying out a cooling and pressing step to apply said molding pressure to said pair of molds having the lens-form body placed therebetween while cooling the lens-form body until the temperature of the lens-form body is lowered to a second predetermined temperature lower than said first predetermined temperature to obtain a final lens product; and   taking out the final lens product from the space between said pair of molds after the product has further cooled down,   wherein the molding pressure is reduced or made zero at least once during each of (a) the heating and pressing step but before the end of the heating and pressing step, (b) the time immediately after completing the heating and pressing step, but before the begining of the cooling and pressing step, and (c) the cooling and pressing step, and wherein when the molding pressure is reduced or made zero during the heating and pressing step the body of the lens material is kept in contact with each of said molding surfaces of said pair of upper and lower molds during the entire heating and pressing step.   
     
     
       2. A method as claimed in claim 1, wherein the molding pressure is set such that gas having a compressed gas pressure and generated inside any space which exists between each of said mold surfaces of said pair of molds and the body of lens material is released, due to said compressed gas pressure, from said space between each of the mold surfaces of the pair of molds and the body of lens material when said molding pressure is reduced or made zero. 
     
     
       3. A method as claimed in claim 1, wherein the relationship between a radius Rm of the molding surface of each of said pair of molds and a radius Rg of an end surface of the body of lens material is expressed by Rg>Rm. 
     
     
       4. A method as claimed in claim 3, wherein the body of lens material is a cylindrical body. 
     
     
       5. A method as claimed in claim 1, wherein the process is performed under conditions for causing the upper and lower molds always to be in contact with the lens material from the beginning of the preheating step to the end of the cooling and pressing step. 
     
     
       6. A lens molding method for press-molding a body of lens material placed in a space between mold surfaces of a pair of upper and lower molds by applying a molding pressure to the pair of molds to produce a lens, comprising: placing said body of lens material in a space between said mold surfaces;   carrying out a preheating step for heating the body of lens material placed in the space between said mold surfaces of said pair of molds until the temperature of said body rises to a first predetermined temperature;   carrying out a heating and pressing step to apply said molding pressure to said pair of molds having the body of lens material placed therebetween while keeping the temperature of said body at the first predetermined temperature of said body at the first predetermined temperature thereby to mold said body into a lens-form body;   carrying out a cooling and pressing step to apply said molding pressure to said pair of molds having the lens-form body placed therebetween while cooling the lens-form body until the temperature of the lens-form body is lowered to a second predetermined temperature lower than said first predetermined temperature to obtain a final lens product; and   taking out the final lens product from the space between said pair of molds after the product has further cooled down;   wherein the body of the lens material is always keeps in contact with each of said molding surfaces of said pair of upper and lower molds during a time from the beginning of the preheating step through the end of the cooling and pressing step, and wherein the molding pressure is reduced or made zero at least once during the heating and pressing step but before the end of the heating and pressing step.   
     
     
       7. A method as claimed in claim 6, wherein the molding pressure is set such that gas having a compressed gas pressure and generated inside any space which exists between each of said mold surfaces of said pair of molds and the body of lens material is released, due to said compressed gas pressure, from said space between each of the mold surfaces of the pair of molds and the body of lens material when said molding pressure is reduced or made zero. 
     
     
       8. A method as claimed in claim 7, wherein the relationship between a radius Rm of the molding surface of each of said pair of molds and a radius Rg of an end surface of the body of lens material is expressed by Rg>Rm. 
     
     
       9. A method as claimed in claim 8, wherein the body of lens material is a cylindrical body.